Referring to FIG. 1, a typical wireless telecommunications system divides a geographical area into a plurality of cells 10 each of which comprises one or more base stations (Node B), wherein mobile user devices (UE1, UE2, UE3) located within a cell 10 communicate with the base station (Node B) of that cell 10. More specifically, a base station (Node B) handles radio transmissions and reception to and from mobile user devices (UE1, UE2, UE3) over radio channels (R1, R2, R3), and is controlled by a radio network controller (RNC) that is connected to a core network (20). A transmission from a base station (Node B) to a mobile user device (UE1, UE2, UE3) is known as a downlink transmission. Similarly, a transmission from a mobile user device (UE1, UE2, UE3) to a base station (Node B) is known as an uplink transmission.
The Worldwide Interoperability for Microwave Access (WiMAX) protocol (IEEE 802.16 standard) is a wireless communication protocol, which employs Orthogonal Frequency Division Multiple Access (OFDMA) in combination with Time Division Multiple Access (TDMA). Orthogonal Frequency Division Multiplexing (OFDM) subdivides a high data rate input data stream into a number of parallel sub-streams of reduced data rate wherein each sub-stream is modulated and simultaneously transmitted on a separate orthogonal sub-carrier. In Orthogonal Frequency Division Multiple Access (OFDMA) sub-carriers are grouped into sub-channels, wherein in order to mitigate the effects of frequency selective fading, the carriers in a given sub-channel are spread along channel spectrum. In the hybrid OFDMA/TDMA approach, transmission channels are divided in the frequency domain into a plurality of sub-carriers and are divided in the time domain into time slots of fixed or variable duration. In other words, each time slot contains a data segment (of OFDM symbols) of fixed or variable size (whose size depends on the chosen modulation/coding method of the transmission channel), wherein these data segments (or slots) represent the smallest accessible portion of the network resources provided by the OFDMA/TDMA approach, which are managed by a MAC protocol.
Thus, referring to FIG. 2, a WiMAX frame can be modelled as a matrix Mεm×n with m (sub-channel) rows and n (symbol) columns, wherein an individual element of the matrix M is a slot s(i, j), i=0 . . . m−1, and j=0 . . . n−1, wherein the WiMAX physical layer provides m and n as part of the characteristics of the frame matrix. In practice, rather than each cell containing a waveform, the cells contain coefficients representing the waveforms, wherein the coefficients are derived from a Fast Fourier Transform (FFT). The number of bits encoded by a given wave form depends on the modulation coding scheme (MCS) employed by each waveform.